Composition for deanodizing aluminum and aluminum alloys



Patented Apr. 9, 1946 UNITED STATES PATENT OFFICE COMPOSITION FOR DEAN ODIZING ALUMI- NUM AND ALUMINUM ALLOYS Joseph Janota, Jr., Crete, and Bland B. Button,

Jr., Chicago, IlL, assignors to The Diversey Corporation, a corporation Illinois a No Drawing. Application February 9, 1945, I

Serial No. 577,152 a 1 Claim.

This invention relates to a composition of matter and more particularly to a dry mixture of hemi-sodium phosphate and chromic acid adapted for use in deanodizing aluminum and aluminum carboys and is impracticable from an economical and commercial viewpoint as compared with the present composition which can be dispensed, shipped, and stored in solid form.

alloys. 5 The present composition consists of a dry mix- One of the standard methods of treating aluture of approximately 80% hemi-sod ium phosminum or aluminum alloy materials now in use phate (NaI-LzPOtHaPOU and zm'hromic acid. is the anodizing process. In this process the alu- (CrOz) .mfimai is added to water when minum articles are immersed on aluminum racks it is desired to use it, preferably at the rate of 12 in a bath of the electrolyte, and an anodizing oimces per gallon of water. The solution is emcurrent passed therethrough. Eventually the ployed at about 180 F. and will completely strip racks themselves acquire a heavy odized coatthe anodized film from the aluminum racks withing. This coating has a high electric resistance in 3 to 10 minutes. The alum n is left bright and forms an insulation. The racks themselves and free from smut and is not corroded. are part of the electric circuit so that as the 15 The proportion of hemi-phosphoric acid maybe anodized coating builds up it interferes with the somewhat reduced, but as it is loweredit takes passage of electricity. Periodic stripping of this longer to strip the anodized coating. The chroanodized coating is, therefore, a requisite of the mic acid appears to be used up in the removal process. of the anodized film. It also acts to prevent cor- Various corrosive materials have been employed rosion by the phosphoric acid. The proportion of in the past for such stripping operation. The chromic acid, therefore, should not be reduced requisites of a suitable stripping bath are: greatly below the 20% limit. The proportion may,

(1) Ability to remove the anodized coating howevenbe somewhat increased. within a short period of time, generally less than The foregoing detailed description has been 15 minutes. given for clearness of understanding only, and no (2) Ability to leave the resulting surface bright unnecessary limitations should be understood and free from smut. therefrom.

(3) Non-corrosiveness to the underlying alu- What we claim as new, and desire to secure by minum. Letters Patent, is:

No combination of solid materials has hereto- A dry mix consisting essentially f hemifore been available which will satisfy all three of the above requirements. A mixture of liquid phosphoric acid and chromic acid may be employed satisfactorily but it must be handled in sodium phosphate and 20% chromic acid.

JOSEPH JANOI'A, JR. BLAND B. BUTTON, JR. 

